Method of reading bistable storage tubes by increasing luminescence where information is stored

ABSTRACT

In a method of providing a stable bright direct view of information stored in a bistable storage tube the storage surface of the tube is swept with an electron beam of an intensity not sufficient to write for producing electrical signals corresponding to the information that has been stored in the storage surface, an electron beam from a read out electron gun of the storage tube is controlled with the electrical signals to supply a large current to the read out portions in the storage surface having information to cause them to luminesce brightly and above described cycle is repeated until the entire area of the storage surface is read out.

g 151 3,693,4l40 51 Sept. 19, 1972 [54] METHOD OF READING BISTLE 3,413,513 11/1968 Donoghue ..315/13 ST S'EO GE T st-L BY INCREASING LUMHNESCENQE HERE Primary Examiner-Stanley M. Urynowicz, Jr.

INFORMATION IS STO &= I) Assistant Examiner-Stuart Hecker {72] Inventor: Hajime Tam, Tokyo Japan Att0rneyCh1tt1ck, Pfund, Birch, Samuels & Gauthier [73] Assignee: lwatsu Electric Company Limited, [57] ABSTRACT T k ,.I 0 yo apan In a method of providing a stable bright direct view of P116111 1970 information stored in a bistable storage tube the [21] AWL No; 98,562 storage surface of the tube is swept with an electron beam of an intensity not sufficient to write for producing electrical signals corresponding to the information "315/12, 7 /56 l 2 9/ 5% that has been stored in the storage surface, an electron c J beam from a read out electron gun of the storage tube [58] Field of Search ..340/l73 CR; 315/13 ST, 12 is Controlled with the electrical signals to pp y a large current to the read out portions in the storage [56] References Cmd surface having information to cause them to luminesce UNITED STATES PATENTS brightly and above described cycle is repeated until the entire area of the storage surface is read out. 3,214,516 10/1965 Anderson ..315/12X 3,491,236 1/1970 Newberry ..340/ 173 CR 3 Claims, 2 Drawing Figures STEP wnvr GENERATOR OOOOOOOO OOOOOOOO a 11 10 9- PULSEGENERATOH AMP DISGRIMIHATDR AMP PATENTEUSEP 19 m2 F/GZ OOOOOOOOnwOOOOOOOO INVENTOR HAJIME TAKITA BY m ATTORNEY S BACKGROUND OF THE INVENTION This invention relates to a method of reading a bistable storage tube by means of a writing electron gun thus readily providing clear direct readings.

In a bistable direct viewing storage tube thus having a storage insulator layer of phosphor for utilizing the secondary electron emission characteristic thereof, it has been difficult to obtain clear reading. Because, as phospher is used to compose the storage insulator, reading out of information stored therein is made possible only by electrons emanated from a low speed flood type electron gun.

Although it is clear that clear and bright read out is possible by increasing the energy level of the electrons emanated from the low speed flood type electron gun, patterns or information that have been written in an extremely short time of less than one second would be spreaded or diffused, thus rendering them difficult to read. On the contrary, decrease in the energy level of the electrons from the flood type electron gun results in the erasion of the stored information. Thus, the energy level of the electrons from the flood type gun that assures stable read out is about 200 volts which is much lower than the high voltage of about 3,000 volts utilized for storing information in the storage surface. Con sequently, the luminescence of the phosphor is very weak and dark.

For this reason, it is clear that the intensity of the electron beam emanated from the flood type electron gun should be increased for the purpose of providing clear read out. However, there arises such difficulty that in view of the shortage of the capacity of a single electron gun it is necessary to incorporate two or more guns into a single cathode ray tube thus complicating the construction thereof. Moreover, in a cathode ray tube having a large storage area it is necessary to employ a great number of flood type electron guns for the purpose of providing the same current density per unit area of the storage surface, thus further complicating the construction. Another difficulty lies in the generation of ions. The percentage of ionization of the gas molecules remaining in the tube by the flooded electrons emanated from the gun increases with the number of electrons. However such ions are attracted by the storage surface to write portions thereof which are not intended to have information. In other words, the writing operation of the desired information also stores ions on those portions not intended to have information thus increasing ground noise and hence degrading contrast. Consequently, the interval during which read out is possible is decreased further. For this reason, the number of guns that can be employed is limited.

SUMMARY OF THE INVENTION It is an object of this invention to provide a novel method of reading a bistable storage tube without the defects described above.

According to this invention there is provided a method of reading a bistable storage tube comprising the steps of sweeping the storage surface of the bistable storage tube with an electron beam of an intensity not sufficient to write for producing electric signals corresponding to the information that has been stored in the storage surface, controlling an electron beam from a read out electron gun of the storage tube with the electric signals to supply a large current to the read out portions of the storage surface having information to cause said portions to luminesce brightly and the above described cycles until the entire area of the storage surface is read out.

BRIEF DESCRIPTION OF THE DRAWING The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawing in which FIG. I is a plot to show secondary electron emission characteristics in a bistable direct view type storage tube having a write-read electron gun and a flood type electron gun, and

FIG. 2 shows a bistable direct view type storage tube utilizing the secondary electron emission characteristic and a driving circuit for the storage tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference first to the storing operation of a bistable direct viewing storage tube utilizing a storage insulator of phosphor such a tube utilizing the secondary electron emission of the phosphor having the characteristics as shown in FIG. 1, curve I represents the secondary electron emission characteristic of a write electron gun whereas curve II that of a flood type electron gun. The abscissa of FIG. 2 represents voltage (V). Assuming that the cathode potential VF of the flood type electron gun equals zero and is utilized as the reference potential, the cathode potential of the write electron gun is denoted by VWK, the collector potential of the target by V and the potential of an astable point P representing the first crossover for the flood type electron gun and showing the boundary on the target surface between portions storing and not storing informations by Vpc Then the potential of the portions of the target surface storing informations will have a potential V, whereas the potential of the portions not storing the informations will have a potential of V The ordinate represents the secondary electron emission ratio 8 line L corresponds to 8 1, areas above line L correspond to 8 1 whereas areas below line L correspond to 8 1.

The plot shown in FIG. 1 shows that the potential of the portions written with information is represented by V the secondary electron emission ratio of these portions for the write electron gun equals 1 and that the potential of the portions not written with information is represented by V and their secondary electron emission ratio is larger than unity. It is to be particularly noted that portions written, and not written with information have different secondary electron emission ratios with respect to the write electron gun.

When a write electron beam of small current is impringed upon the portions written with the information and the portions not written with the informations while the storage tube is being maintained at two stable points P and P by a flooded beam, owing to the small intensity of the beam, portions not written with informations will become slightly positive with respect to the write beam because these portions have a secondary electron emission ratio of larger than unity. However, the potential of the portions not written with information will become slightly positive with respect to the write beam because these portions have a secondary electron emission ratio of larger than unity. However, the potential of the portions not written with information will be restored to their inherent potential V by the electrons from the flood type electron gun unless the intensity of the beam is sufficiently high to exceed the potential V of the astable point P,,. On the other hand, when irradiated with electrons, portions written with the information will emit secondary electrons, the potential thereof would not be varied by the electron beam because these portions have a secondary electron emission ratio equal to unity.

Thus, when a write beam of extremely small current is caused to impinge upon portions written with or not written with information, the potential of these portions will not be varied by the holding action of the flooded beam. But due to the difference in the secondary electron emission ration 6, the current collected by the collector electrode will be different with the result that a current corresponding to the information written in the storage surface can be derived out at output A (see FIG. 2). The quantity of current which is not sufficient to write is herein denoted by a symbol I Based on this analysis, according to this invention the storage surface is irradiated with an electron beam having the same energy level as the write beam thus providing direct reading read out.

In the embodiment illustrated in FIG. 2 there is shown a bistable storage tube 1 comprising a read out electron gun 2, a flood-type electron gun 3 and a target 4. The read out electron gun 2 includes a control grid and a deflection system 6.

The external control circuit comprises a step wave generator 7, a read pulse generator 8, amplifiers 9 and 1 l, a discriminator 10, sources of potentials E E 7 E E and E capacitors C, to C and resistors R and R which are connected as shown.

For the sake of description, it is herein assumed that information is written on target 4 by means of the write beam and that the stored information is preserved by the flooded electrons supplied by flood type electron gun 3. Thus portions of the target written with the information are caused to luminesce by the electrons projected by the flood type electron gun 3. However such luminescense is weak or dark for the reasons described hereinabove.

Under these conditions, the entire surface of the target 4 is swept by an electron beam of a current I of an intensity not sufficient to write. In other words, this beam is the read out beam which is utilized to judge a point as to whether it has information or not while sweeping across the target as will be described later This read beam is swept by a step formed wave but not by a saw tooth wave as commonly used for sweeping an electron beam. This electron beam is moved such that it is held stationary for a certain interval on a point on the target 4 and is then moved to the next point for reading it after a predetermined time interval T More particularly, for a short interval I when the read beam is moved to the new point by the action of the step wave supplied from the step wave generator 7 to the deflection system 6 current I is passed through target 4 to effect read out. As a result of read out a current pulse is derived out which is amplified by amplifier and then supplied to a descriminator 10. Discriminator 10 determines whether the read out point has information or not. when discriminator w determines that information has not been written at this point, no signal is sent to the control grid 5 of the read electron gun 2 so as to maintain it under the cut off state. After elapse of an interval T corresponding to one step wave applied to the deflection system 6, a step wave designating the next read position is applied to the deflection system 6 to address a new position to be read while at the same time a positive pulse voltage is supplied to control grid 5 from pulse generator 8 for directing the beam of current I to the new position.

In this manner, when a portion is read out and when it is determined that this portion has information, a positive pulse is applied to control grid 5 of read out electron gun 2 for applying to target 4 a current of a valve required to write an information in that portion. Thus, since a current much larger than the current I which is insufficient to write is sent through target 4, the portion that has been determined to contain an information is made to luminesce brightly. This current continues until immediately before a signal designating the next position to be read is applied to the deflection system 6. In this manner, as the interval T elapses, the next position to be read out is reached, and this cycle is repeated until the entire surface of target 4 is read out. When this read out operation by raster is carried out at a frequency of 30 times per second, stable and bright direct read out of the stored information becomes possible.

The reason that a step wave is used in the foregoing embodiment is that if the beam is swept by a saw teeth wave, the information-containing position that initially receives the read current I will not be that position which receives the large current which is generated in response. Thus, information would be written in portions other than those required to be written, and when this operation is repeated the stored information would be broadened in the direction of sweeping of the raster. However, even the saw tooth wave may be used provided that due consideration is paid to avoid the defect just mentioned. Thus, for example, it is possible to sweep with the saw tooth wave until a portion written with an information is reached, to stop sweeping and cause that portion to luminesce, and then continue to sweep with the saw tooth wave until the next portion written with information is reached.

Instead of utilizing the above described bistable storage tube having a target with a storage surface of phosphor, it is possible to use another bistable direct viewing storage tube of well known type utilizing a mesh coated with a non-luminous storage insulator.

As above described, since according to this invention, the storage surface of a bistable storage tube is swept with a raster of a current of a valve insufficient to write, only when a portion written with information is reached, a read out gun is controlled by a signal read out from that portion, and a large current is supplied to the portion just read out to cause it to luminesce brightly, it is possible to obtain bright read out without affecting the portions other than those to be read out and without disturbing the stored information. For this reason, the flood type electron gun is only required to preserve the stored informations so that it becomes possible to reduce the current of the flooding beam. Moreover, it is not necessary to provide a plurality of flood type electron guns. Further, as the large current necessary to realize bright read out can be provided with an electron beam of a comparable intensity as that required for writing, (for example, an electron beam of about 3,000 volts), even when the quantity of a secondary electron emissive material other than the phosphor, (for example magnesium oxide, which is admixed with the phosphor for increasing the speed to writing) is decreased, it is possible to still obtain bright read out. in other words, higher write speed is possible.

Normally, as it is necessary to use only a small cur: rent, the tendency of creating ions is greatly reduced thus providing high contrast read out over a long time.

While the invention has been shown and described in terms of a preferred embodiment thereof, it will be understood that many changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.

What is claimed is: l. A method of reading a bistable storage tube comprising the steps of sweeping the storage surface of said bistable storage tube with an electron beam of an intensity not sufficient to write for producing electric signals corresponding to the information that has been stored in said storage surface, controlling an electron beam from a read out electron gun of said storage tube with said electric signals to supply a large current to the read out portions of said storage surface having information to cause said portions to luminesce brightly, controlling said electron beam to supply said large current for a predetermined time to each said read out portion of said surface having information and repeating above described cycle until the entire area of said storage surface is read out.

2. The method according to claim 1 wherein said electron beam is moved across said storage surface by a step wave.

3. The method according to claim 1 wherein said electrical signals are applied to a descriminator to determine whether said read out portions have been written with information or not and when said signals indicate that said read out portions have been written with information a pulse signal is supplied to said read out electron gun to cause the same to supply to said read out portions an intense electron beam thus causing said read out portions to luminesce brightly. 

1. A method of reading a bistable storage tube comprising the steps of sweeping the storage surface of said bistable storage tube with an electron beam of an intensity not sufficient to write for producing electric signals corresponding to the information that has been stored in said storage surface, controlling an electron beam from a read out electron gun of said storage tube with said electric signals to supply a large current to the read out portions of said storage surface having information to cause said portions to luminesce brightly, controlling said electron beam to supply said large current for a predetermined time to each said read out portion of said surface having information and repeating above described cycle until the entire area of said storage surface is read out.
 2. The method according to claim 1 wherein said electron beam is moved across said storage surface by a step wave.
 3. The method according to claim 1 wherein said electrical signals are applied to a descriminator to determine whether said read out portions have been written with information or not and when said signals indicate that said read out portions have been written with information a pulse signal is supplied to said read out electron gun to cause the same to supply to said read out portions an intense electron beam thus causing said read out portions to luminesce brightly. 